Highly purified Alpha-thrombin, plasmin, cathepsin G, chymotrypsin, trypsin and urokinase were incubated with laminin, type IV collagen and type V collagen. At 25 C (1:100 enzyme to substrate ratio on a weight/weight basis) Alpha-thrombin selectively degraded the Beta chain of the native laminin, whereas plasmin cathespin G, trypsin and chymotrypsin degraded both the Alpha and Beta chains. The specific limited cleavage fragments of laminim produced by Alpha-thrombin and the other enzymes were purified by HPLC, studied electron microscopy and evaluated for biologic activity. A model was proposed for the structure of laminim and which domains of the molecule mediate various biologic functions. A cell receptor for laminim was identified.